Unusually deep earthquakes in the central Sierra Nevada (California, USA): Foundering ultramafic lithosphere?
Bibliographic record
Abstract
Abstract Using a network of temporarily deployed broadband seismometers, we characterize an unusual region of crustal earthquakes in the west-central Sierra Nevada, California (USA). We locate 131 earthquakes, which occurred from 3.1 to 47.1 km deep during June 2005 to May 2006. We detect more events, at greater depths, than are present in the Northern California Seismic Network catalog during this period. Most of the events occur at depths of 20–35 km and cluster into two distinct groups. In addition, some of the events appear to be repeating due to the similarity of their waveforms and locations. We calculate focal mechanisms for 52 of these events, and about half exhibit reverse faulting, which represents a state of horizontal compressional stress that is distinct from the regional stress field. From first arrivals, we calculate a one-dimensional model of crustal P-wavespeeds, which resolves a gradational increase from 5.8 km/s near the surface to 6.7 km/s at 35 km depth. The events overlie a significant variation in the character of the Moho, and two long-period events occur near the seismically imaged Moho at nearly 40 km depth. We suggest that these earthquakes could be the seismogenic response of the crust to active foundering of mafic-ultramafic lithosphere and resultant asthenospheric upwelling beneath the central Sierra Nevada.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".